In hybrid automotive vehicles comprising a primary power source, such as an electric motor powered by a rechargeable battery pack, and a secondary power source, such as an internal combustion engine (ICE), it is known to provide a system for controlling the initiation of the secondary power source, the ICE. Such control systems are provided to automatically initiate the ICE in situations where the electric motor is not able, on its own, to deliver sufficient drive power (drive torque) for the vehicle. Typically an ICE is automatically initiated in dependence upon a current driver demanded torque and when a driver demanded torque reaches a threshold, the ICE is initiated. In some vehicles an ICE is initiated in dependence upon a current pitch of the vehicle which can be used to determine that the vehicle is, for example, driving up an incline that is considered sufficiently steep that supplementary torque from the secondary power source needs to be delivered.
The present invention seeks to provide an improvement in systems for controlling hybrid vehicles that has particular application for hybrid electric vehicles (HEVs) having a primary electric power source and a secondary internal combustion engine power source. The invention may be utilised in applications other than for hybrid automotive vehicles, and may be utilised in hybrid vehicles having other combinations of power source.